1. Field of the Invention
The invention is related to email systems, and more particularly, to a method for efficiently migrating a mailbox to a new mail server.
2. Related Art
A mail server (or “email server”) provides email handling for one or more users. The mail server receives and stores email messages for a particular user in one or more mailboxes that are specific to that user. It is often desirable to migrate a user's mailbox to a different mail server (e.g., to increase mail storage capacity or to upgrade server hardware/software). Mailbox migration refers to copying the messages in an existing mailbox to a new mailbox on a new mail server so that the user can access his or her email from the new mail server.
FIGS. 1A-1D depict stages in a conventional mailbox migration process. FIG. 1A depicts a conventional email system, in which a router R1 routes email messages MAIL to a mailbox MB1 on a mail server MS11. Those messages can then be accessed by a user via an email client CL1. Router R1 and email client CL1 address mailbox MB1 based on an address stored in a directory D1. Control over the process in which mailbox MB1 is migrated from (source) mail server MS11 to a (destination) mail server MS12 is provided by a control terminal T1.
In FIG. 1B, terminal T1 sends a signal LOCK to mail server MS11 to lock mailbox MB1 to prevent any interaction with the messages contained within mailbox MB1 (as indicated by the large “Xs” over the communication path between router R1 and mailbox MB1, and over the communication path between client CL1 and mailbox MB1). Then, in FIG. 1C, terminal T1 sends a command COPY to server MS11 to cause the messages in (locked) mailbox MB1 to be copied over to mail server MS12 as messages in a new mailbox MB1′.
Meanwhile, the address stored in directory D1 for mailbox MB1 is updated to reflect the address of mailbox MB1′ on mail server MS12, so that both router R1 and client CL1 are directed to access mailbox MB1′. Thus, when terminal T1 sends an unlock command UNLOCK to mail server MS12, as shown in FIG. 1D, router R1 begins delivering email messages MAIL to mailbox MB1′, while client CL1 provides access to the messages within mailbox MB1′.                In this manner, mailbox migration from mail server MS11 to mail server MS12 can be accomplished in a relatively straightforward manner. Unfortunately, because the user is locked out of his or her mailbox as it is being copied from mail server MS11 to mail server MS12, the conventional migration process shown in FIGS. 1A-1D can be quite disruptive to the user associated with mailbox MB1 (and mailbox MB1′).        
For a large mailbox, the copying step depicted in FIG. 1C can take anywhere from several hours to several days. This extended period of email downtime can be quite problematic for users that depend on continuous access to email. Other conventional mailbox migration methods typically require a similar level of downtime.
Accordingly, it is desirable to provide a method and apparatus for migrating mailboxes that minimizes disruptions in email access.